Numerous devices and techniques have been used to improve the safety of vehicle operation, both for vehicle operators/passengers and those in the environment around a vehicle. Additionally, devices and techniques are also employed to reduce or eliminate the likelihood of damage to a vehicle and objects in a vehicle's environment during vehicle operation. Many of these devices and techniques focus on providing a vehicle operator with information about potential hazards so that the operator has ample time to take corrective measures. For example, many automobile manufactures equip vehicles with single or multiple beam radar back-up warning devices. These devices are designed to assist a driver in detecting animals, people, vehicles, and other objects when backing the vehicle. Radar has also been used in many experimental forward-looking obstacle detection and collision avoidance systems. Other areas of obstacle detection/avoidance research and development include ultrasonic systems, video systems, and lidar (light detection and ranging) systems.
In any of these systems, it is desirable for such systems to employ sensing techniques for object detection and tracking that have relatively high resolution for obstacle localization, precise tracking capabilities, and reliability under many different driving conditions. Lidar based systems have some advantages such as precise distance measurement, high angular resolution, low latency, and relatively low system complexity.
Lidar systems currently developed for vehicle-based object tracking/avoidance systems typically deploy a pulsed (or suitably shuttered continuous wave) laser beam that is scanned in the direction of interrogation using a moving mirror, such as a rotating single-facet or multi-facet (e.g., polygonal) mirror. The laser beam is reflected from an obstacle and detected with a photodetector. The time-of-flight of the laser pulse, i.e., the time delay between the transmitted pulse and the received pulse, determines the object distance. The object's bearing is further determined based on the mirror's angular position at the time of the transmitted pulse.
Such lidar systems offer a degree of simplicity in their design, but their implementation presents certain disadvantages. Chief among these disadvantages is the presence of a moving mirror that is typically rotated at a rate of tens or hundreds of revolutions per minute. These rotating mirrors and corresponding motors add size and weight to the device, the motors can require significant power, and the presence of moving parts can increase the likelihood of device failure through mechanical wear. These are all disadvantages in general, and particularly so in the context of vehicle deployment. Vehicles are expected to operate in environments and manners that can be harsh for devices that include high-speed rotating mirrors, e.g., operation on course roads, rapid acceleration/deceleration, etc. Moreover, for many vehicles, particularly automobiles, it is desirable to locate lidar devices in perimeter positions that consume as little space as possible and are otherwise unobtrusive, e.g., behind an engine grill, integrated into a headlight or taillight assembly, or integrated into some portion of a bumper.